A laser machining device that machines a workpiece by irradiating the workpiece with a laser beam guides a laser beam emitted from a laser oscillator onto the workpiece along a predetermined optical path. When it is necessary to make an optical length variable for a reason of focusing or the like, then the laser machining device is provided with a bellows device including a extensible and contractible cylindrical bellows, and the bellows device is configured to have a bellows surrounding the optical path and to allow the laser beam to advance within the bellows.
When the optical path is misaligned, the bellows meanders, or a laser beam is reflected by a workpiece or the like and applied on a bellows surface for some reasons, the bellows may be carbonized (burned), damaged, and bored. Furthermore, also in a case where melts (sputters) generated during laser machining are scattered and attached to the bellows, the bellows may be carbonized and damaged.
Therefore, as disclosed in Patent Literature 1, an attempt has been made to weave lead wires into a bellows and to detect damage to the bellows based on the change in conductive state of the lead wires.
Furthermore, as disclosed in Patent Literature 2, when smoke detecting means having a light emitting diode and an optical sensor provided in a bellows, smoke generated when the bellows is carbonized can be detected, and thereby it is possible to detect damage to the bellows.